Not sure what accuracy you are after but I often infill my points by contouring then use a choice of Cad options.
I 'm not aware of an automated way of densifying the points you allready have.

If you set the contour interval at an approximate setting that gives the required density of infill you can then create a series of polylines that can be give points at the vertices - 'Autoadd points'. One needs to be aware of the quality of result and all that entails - speaks for itself in that area.

Other obvious option- physically pick points (Editp and Pick point) by guestimation between known points.